Tuning indicator system



Aug 17, 1948. H. L. BLAlsDELL TUNING INDICATOR 4SYSTEM 3 Sheets-Sheet l4 Filed Oct. 29, 1945 ATTORNEY Aug. 17, 1948. H. BLAlsDELl. 2,447,309

` TUNING INDICATOR SYSTEM Filed oct. 29, 1945 3 sheets-sheet 2Frequencys INVENTOR.' HAROLD L. BLAISDELL @Zie/- Aug. 17, 1948 H. l...BLAlsDELL TUNING INDICATOR SYSTEM 5 Sheets-Sheet 3 Filed Oct. .29, 1945l INVENToR. HAROLDV L. BLAISDELL 'BY 1 ATTORNEY Patented ug. 17, 194gUNITED QFFI 1 L n I V2,447,309 K I f v INDICATOR SYSTEM Harold L.B1aisae11,-1.;itue Neck, N. YQ, assignor,

by mesne assignments,Y tu 1 Hazelille Riisel'h, ylnc., Chicago.' Illa acorporation 0f illinois Apiiation octlfr 129, 19`15, seria1 No, 625,159c The present invention relates-to tuning indicator systems forWave-signal 'receivers and, 'particularly, to such systems forindicating the degree of mistuning of the receiver oneither side ofjareceived Wave signal or for indicating` the degree and direction ofsuch-mistuning.

Wave-signal receivers conventionally are pinovided with adjustabletuningelementsbywhich the receiver may be tuned toy a desiredWave sig-Tuning indicator systems Eheretofore Aus'edior` proposed foramplitude-modulation -receiversinl clude some device for visuallyindicating thelmagnitudeof a unidirectional current or voltagederivedfrom the wave signal translated by .ther-e'- ceiver and varying with itsamplitude. j Tuning -indicator systems for Afreq''u'e'ncy-modulationfreceivers are somewhat similar to 'those `for#ampli-- tude-m'odulationreceivers except for the imanner of deriving the tuning indicatorcontrol'ipo'- tential. Thelatter is usually so'delrived-that'theamplitude and polarity ofthe lpotenltial'varies with the degree 4anddirection, respe'ctively,-o-f

mistuning of the receiver to the desired Mvvaves'ignal.' All such 'priorindicating *systems are :so arranged that the magnitudeof indicationprovided by the system varies directly' with the intensity of a receivedWave signal as translated to. the

"point inthe receiver where thetuning indicator This is because thehighest sensitivity of the`sys. tem mustbe reservedfor those-wavesignals-having thelargestintensties to be encountered in the operationof the receiver. f i 1 -1 It is -an'object ofthe present'v invention,therefore; to provide anew and improved tupingindivcater system,'for aWave-signal receiver includinglan adjustable Ytuningl means, whichVavoids oneor moreof the disadvantages and limitations of Aprior suchsystems. .l

It is'a further object .ofthe inventionto provide a tuningindicatorsystem which has. an indicating sensitivity varying inverselywith vthe -intensity Aoi? received Wave signals.. s

It iis anadditional object yof theinvention to provide r a i tuningindicator ,system which vprovides .approximately the same magnitude ofVindication overa `Widecrange of received wave-signal intensities.

IItfis a further objectoi 'the ,invention to providea new and'improvedtuning-indicator, sys,

tem, for a wave-signalV receiver including aniad- .instable tuningmeans, of simple and inexpensive circuit .arrangement involving .aminimum of circuit components.

In accordance With Vaparticular form of the invention, a tuningindicator system, for ,awaver signal. receiver :including an 'adjustablez tuning means, comprises an inputicircuitadapted t9' have .appliedthereto-a unidirectional control signal ,the -magnitude ofcwhich `variesVWith the degree .of

mistuning of the .receiver .oneither side of a re-v ceivedfwave'signal,`and -a ltuning `indicator Vcoupled to` the input circuit; ,andresponsive .to the .control vsignal for indicating [such-,degree ofmisftunin'g. The system includes .meansfor deriving a control effect,themagnitudeoi which varies muchless rapidlyrwith the aforesaiddegl-leof Imistuning than .doestheaforesaid control vvSignal,

-isignal .receiver .embodying:thefprcsent enligne@ inaparticularformkFss- 2am@ dmprse'u ...es

Referring now more particularly to Fig( lof" the drawings, there isrepresented, partly sche.- matically,

a complete frequency-modulation' wave-signal receiver of aconventional#design unidirectional tuning control signal the magnitudeof which varies with the degree of mistuning of the receiver on eitherside of the received Wave signal and the .polarity of which varies withthe direction of such mistuning. Where the unit l5 includes aconventional limiter to limit amplitude variations of a received wavesignal, the control signal applied tothe input terminals 20 also varieswith the intensity of the wave signal for all values thereof less thanthe limiting level.

- This condition occurs, for example, when receiv- Aing -wave signalsfrom comparatively distant transmitting stations.

It is the purpose of the "'presentinvention to provide tuningindications embodying the present invention in aparticular form. Thereceiver is shown as including a tun-Vi able radio-frequency amplifier Ihaving an in?` put circuit coupled to an antenna system II, I2 andhaving an output circuit coupled to a tunable frequency lchanger oroscillator-modulator I3. Connected in cascade with theAoscillator-modulator I3, in the order named, are anintermediatefrequency amplier I4, a combined single-stage or multi-stageintermediate-frequency lampliiier and automatic-volume-control or A. V.C. supply I (which may, if desired-include a conventionalamplitudelimiter), a frequency detector IB, an audio-frequency amplifierI'I, and a sound reproducer I8. As is conventional in such receivers,the units I0 to I6, inclusive,` have a relatively broad `band-.passcharacteristic which may, for example, be 150 or 200'kilocycles wide.V Atuning indicator system, presently to be described in greater. detail,includes a tuningy indicatory device I9 is coupled to the output circuitof the frequency detector I6. The automatic-,volume-control supply ofunit I5 has an output circuit, designated as A. V. C., coupled to theinput circuit of one or more of the .tubes of units I0, I3, I4, andI5.in conventional manner.

It will be understood that the various units just described may, withthe exception of the tuning indicator system, be of'aconventionalconstruction` and operation, the details of vwhich are Well known intheart, rendering further description thereof unnecessary. Consideringbriefly the operation of the receiver as a whole, and neglecting forythe moment the operation of lthe tuning indicator system presently toAbe described, a desired frequency-modulated wave signalis selectedandamplied by the'tunable radiofrequency amplifier I0, converted to afrequencymodulated intermediate-frequency Wave signal in theoscillator-modulator I3, amplified in the intermediate-frequencyamplifiers I4 and I5, and detected by the frequency detector IE, therebyto derive the audio-.frequency modulation components thereof. Theaudio-frequency components, are in turn, amplified in theaudio-frequency amplifier I1 and are reproduced by the sound reproducerI8 in conventional manner. An auto- -matic-volume-control or A. V. C.bias derived by the A. V. C. supply system of unit I5 is effective tocontrol the amplification or gain of one or more of the units I0, I3 orI4 to maintain the signal input to the detector I6 within a relativelynarrow range for a' widerange of received signal intensities. YReferring now more particularly to the portion of the wave-signalreceiver embodying the present invention, the tuning indicator systemincludes an input circuit, comprising input-circuit terminals 20,vadapted to have applied thereto-'a kintermediate-frequency 'ampliiiercludes a vacuum-tube repeater 34 having input 'ofxapproximately the samemagnitude for reception from such stations as for reception from lessdistant stationswhich, because of the larger intensities of theirreceived wave signals, cause amplitude limiting to be effected by :thelimiter. Ii no limiter is provided in the unit I5, the magnitude of thesignal applied to the input terminals varies, `for any degree ofmistuning, with the intensity of the received wave signal but over avmuch wider range of intensities than occurs when a limiter is used. Thetuning'indicator system also includes the tuning indicator I9 which iscoupled through an amplier and phase inverter 2l to the input terminals20 and is responsivev to the tuning control signal applied thereto forindicating the degree and direction of mistuning of the receiver to thereceived wave signal.- In particular, the indicator I9 is of thecathode-ray tube type having an anode or target electrode 22 andincluding input electrodes comprising a cathode 23 and a .pair rofcathode-ray beam deiiecting electrodes 24 and 25. The deflectingelectrodes 24 and 25 of the indicator tube I9 are directly connectedrespectively to a screen electrode 26y and an anode 21 of tube 2 I thescreen electrode 26 and anode 2l being energized from a source ofpotential, indicated as +B, through respective resistors 28 and 29. Thetube 2| includes a pair of input electrodes, comprising a suppressorelectrode 30 and a cathode 3l, which are coupled through a lter networkincluding aseries-arm resistor 32 and a shunt-arm condenser 33 to theinput-circuit terminals 20. The indicator system thus far described isof the type shown and described in the United States Letters Patent No.2,294,182, granted August 25, 1942 to Robert T. Hintz, for Tuningindicator for carrier-signal receivers, and assigned to the sameassignee as the present invention.

The` tuning indicator system of the present invention also includesmeans for deriving a control effect, the magnitude of which over thepass band of the receiverl varies much less rapidly with the degree ofmistuning of the receiver than does the aforementioned control signal,and for utilizingthe control effect to vary inversely with the intensityof the received Wave signal, by variation of the energization of theanode or target electrode 22 of the indicating tube I9, thesensitivityof response of the indicator I9 to the tuning control signalapplied to the input-circuit terminals 20 to reduce the sensitivity ofindication of the tube IS with increasing intensities of thereceived-wave signal. `This means comprises the I4 which inelectrodes,including a control electrode 35, coupled through a double-tunedband-pass selector 36 to the output circuit of the oscillator-modulatorI3.. The repeater 34 has an anode 31 coupled'through adouble-tunedband-pass selector asto the input circuit 'df the' intermediate-rre;

also' includes means for utilizing the aforementioned control eiect tovary inversely with the intensity, of a receivedfwave Asignal anoperating characteristidnamely the transconductance, of

. the repeater 34,*thereby correspondingly to vary the-gain of theAamplifier I4. This means .comprises `th'e automatic-volume-control biassource oi'"t1'1e'unit I5.: which derives an A. lV. C. bias orcontrol'efect, and the automatic-volume-control circuit, designatedA.,V. C., which is coupled to thexcontrolelectrode 35 of the repeater 34through a=lter network' including a rseries resistor 39 and shuntcondenser 40. The indicator' sensitivitycontrol means additionallyincludes means responsive to variationsiof the operating lcharacteristicof repeater 34, namely, to variations of its transconductance ortovariations of; gain ofthe amplier' ,14; for' controlling in accordancetherewithithe sensitivityoff responseoi the indicator tuberi 9 t'ojthetuningk controlpotential applied to thejinputstcrminalsii to, reduce thesensitivity oi" indicationofth'e indicator tube lil with increasedintensitiesV of the received Wave signal.A They lastmentionedv meansAcomprisesV a positively .energized-screenelectrode 4l; provided in Athe=retionvof3th`ef general operation Voi that portion of the indicatorsystemtwhich includes tubes 19 and 2l,4 isi contained in ;,.theaforementioned Hintz patent Brieflyicon'sidered,. for purposes of thepresentgdescription. assume that the receiver has aff conventional.band-pass characteristic representedibycurves; AzorB of .Fig` 21,: thischaracteristicbein'g relatively nat-topped over a frequency rangeji tozcentered'abo-ut a frequency fnawhi'ch represents the rneaniresonantfrequency of,A the internaediatefrequency` selectors. ofi the ireceiver,for example theiselectors 3S and 38. Curve A is representativev ofv theresponse? for a received vWave signaljof :large intensity While curve vBrepresents the response for ajwave signal of relativelyweal; intensity.Since thegintensityof a received 4Wave signalttranslated te the A.y V.C.' supply of unit` I5 varieswith tuning inl accordancevvithf thebandpassicharacteristic of the receiver, the curves A andfB are alsorepresentative of the variation of the derivedcontrol eiectlor A. V; C.bias-With tuning-of.thereceiveracross; a received wave s` `ialrespectivelyhaving alargeintensity or a Wi kwintensi-ty Ivhefrequency-*response char- Arustic of the 4frequency detector IS isrepresentedby curve C-Vfora-received Wave signal of n GDSY andbyicu'rveD for a' Wave signal Y Y elybvweal; intensity, the detectorrcharac r1icthus being of the familarS congurat'ionfcenteredfuponand varyingrapidly in the region of the mean resonant frequencyffu of the receiver.I e f hevqnlqlli-lthat the receiver isl accurately y y o-a;desired.Waveisignal so that the frediency-Inodulated ,intermediate-frequency wavesignalof the receiver.;hasY amean Wave-signal quencyampliiier'l. VvThelast-.mentioned means 6 frequency' fo'.' Under the foregoing assimedcoiditions, the audio-frequency filter 32, t33` renovs any audio-.frequencymodulation' components rdevelopedin the output circuit of VtheV`frequency detector I-Gf'andfrsin-ce tlieiaveragefoutputlpotential ofthe detector isthen zero as indicated'by either of the curves C or. D,`no unidirectional tuning-control signal is applied to theinputele'c'-trodes 3), 3l of theY tube -2|'. For this operating condition, thevalues of the'screen resistor 28 and anode resistor'29 of thelatter tubeare so selected .with relationA` to the" normal operating; currentsanode 22,` With variation of potential applied to resents the visualindication producedl lay-'mis'- one of the deilecting electrode'si24'or25,. is represented by curve E of Fig. 3. Withequalpotentials applied tothe deecti'ng electr'c'ides',y the resultant shadow angles are equalandthe' deflection' pattern which' appears'on the uorescent anode oftube i9 is symmetrical, as illustratedby the'pattern of Fig. 4a, whereinthe shr-.tdowr angles are `represented bythe dark areas F and-'G and theequal luminous areas are represented by `the light portions H and l?.This syrn'metri'cal pattern provides avisual indication thatthereceiver'is accurately tuned to thereceive'd Wave signa1'.1.V

Assume now that the ,receiver 'is mistuned' to one side of the'received` wave signal; Thezout'- put of the Vfrequency detector iii`novv .hasan averagev unidirectional component of potential the magnitudeof which is dependent rupon-'tite degree of mistuningf and ythe polarityof which i's dependent uponthe direction' of Inistu'ning. Here again theaudio-frequency filter v32, k(i3-removes the audio-frequency modulationcorn-poe nents so that onlythe unidirectionalzcomponent alone is appliedto the input electrodes 30; lfof the tube 2l. If -this unidirectionalpotential has a'positive polarity, it increases the anode current anddecreases the screen-electrode currt-- of the tube 2l thustoincrease*thesoreene'electrode potential and 'decrease `the'anodepotential; The magnitude of such'potentialchange? variesyof course, Withthe magnitude of ythe yunidirection'al potential applied to the inputelectrodes oithe tube 21. The positive V unidirectional potentialsapplied 'to the deflecting electrodes '24 and 25' of the indicator tubelareinow no longerr equal, one having been increasedbv a''certainlamount and the other' having been decreased by approxi:- mately thesame' amount. This unecpllalfenergization of the delecting`electrodes24`and25 produces an unsymmetrical deflectionpatte'rnon thefluorescent anode of theindicator tube" I'Q'i The resulting indicationvis' asindicated by Figs 14D, which represents the visual'indicationpro-l ducedby mistuning of the receiver toorne sido thereceived wave-signal; or Fig.: cwvh'ichr e the direction of mistuning ofthe receiver from the desired .Wavev signal.`

As previously mentioned, the automatic-amplillcation-control or A. V. C.bias derived from the A. V. C. supply of unit I5 is applied through thelter 39, 40 to the control electrode 35 of the vacuum-tube repeater 34so to vary its gain, in conjunction with a similar variation of gain ofunits I or I3 as to maintain the signal input to the frequency detectorI6 within a relatively narrow range for a Wide range of received signalintensities. In so doing, the A. V. C. bias reduces the space current ofthe screen electrode 4I of the repeater 34 with increasing intensitiesof the received wave signal. Since the space current of the electrode 4Iows through the resistor 42 to' develop thereacross a potential drop, itWill be apparent that the positive potential energize.- tion of thescreen: electrode 4I varies' directly with the intensity of the receivedwave signal. However, the anode or target electrode 22 of the indicatortube I9 is energized, through the ener gizing circuit 44, from thescreen electrode 4l of the receiver 34. It will thus be apparent thatthe positive energizing potential applied to the target electrode 22 ofthe indicator tube 9 also varies directly with the intensity of thereceived wave signal.

In the absence of a received wave signal, or when only a weak intensitywave signal is received, little or no A. V. C. bias is developed by unitI5 with the result that the potentials of the screen electrode 4I oftube 34 and the target electrode 22 of the indicator tube I9 haveminimum values.` The electrons emitted by the cathode 23 of the lattertube are attracted to the target electrode '2.2 thereof with relativelylow velocities so that the-electron Ibeam is soft and easily deflectedthrough large angles with small changes-of potentials applied to thedeecting electrodes 24 and 25. The response characteristic of theindicator tube I'9 for a low, but constant, value of target-electrodepotential is represented by curve J of Fig. 3. Increasing the positiveenergization of the target electrode 22, as with increasing values ofA.v V. C. bias consequent upon increasing intensities of a received wavesignal, effects a corresponding increase in the velocity of theelectrons emitted by the cathode 23 and travelling 'to the targetelectrode 22. As a result, the beam becomes stiifer and a larger changeof potential on the deflecting electrodes 24 and 25 is required toproduce a given change of the shadow angle on the uorescent screen ofthe target electrode 22. Each of curves K, E and L of Fig. 3 representsan individual, different response characteristic of the indicator tubeI9 for a given individual, constant value of potential applied to thetarget electrode 22, the several values of potential increasing fromthat for which curve K is representative to that for curve L. Thesecurves make evident the ffact that increasing energization of the targetelectrode effects decreasing sensitivities of the indicator tube,particularly, in that larger vaines of energization malte it necessary'to apply larger values of `control signal to the 'deflecting electrodes24 and 25 to effect a given'change of the shadow angle.

Now it will be apparent that while increasing values of Wave-signalintensity produce larger values of A. V. C. bias and correspondinglylarger positive energizationsv of the target electrode 22 of tube I9,thus to change inversely with the wavesignal intensity the sensitivityof response of the pointed out in connection with curves C and D of Fig.2. As a result, any deviations ofthe mean frequency of a received wave.signal .from the mean intermediate frequency fo, as would occur forexample duringl tuning of the receiver, produce unidirectional tuningcontrol signalslwhich are applied to the tube 2| and thus to thedeflecting electrodes 24 and 25 of the indicator tube I9) the magnitudesof which increase directly 'with the intensity of the received wavesignal. Sucl larger control signals then effectively counteract thedecreasing response sensitivity of the indicator tube I9 and causeapproximately the same change of shadow angle for either strongintensity or weak intensity received wave' signals. y

The value of the screen resistor 42 of the amplier I4 is so selectedwith relation to the screen potential +Sc and the characteristics of thetubes 34 and I9 that the response characteristic ofthe indicator tube I9would be that represented by the broken-line curve M of Fig'. 3 if thechanges of target-electrode potential and changes of tuning controlsignal appliedvto the tube 2| both'were to vary simultaneously andproportionately with the received wave-signal intensity.

This, however, is not the actualoperation of the tuning indicator systemsince kthe derived A. V. C. bias has a value which varies, with 'thetuning of the receiver, as represented by'curves A or B of Fig. 2. TheA. V. C. bias is .thus sub--v stantially constant over thefrequency'range f1 to f2, whereas the tuning control signal variesrapidly in magnitude on either side of the 'frequency fo and over thefrequencyrange f1 to .f2.- The constant value of A. V. C. bias developedover the frequency range f1 to f2 results in a constant value ofenergization of. the target electrode 22 of the indicator tube I9, theexact value ofenergization varying with the intensity of the receivedwave signal as hereinbefore4 pointed out, so that over this frequencyrange the latter tube operates with a response sensitivity Lrepresentedby one of its characteristic curves J, K, E or L of Fig. 3. Thus, as thetuning control signal applied to the tube 2I varies over the frequencyrange f1 to ,f2 in accordance with the characteristie curves C or D ofFig. 2 depending upon the received signal intensity, the entire tuningindication provided by the tube I9 over the same frequency range followsalong one of the-characteristic curves J, K, E or L of Fig. 3 from the90- degree shadow-angle value to a minimum lshadow-angle value at'whichthe particular .sensitivity curve intersects the broken-line curve M.v

A sharp tuning indication is thusprovided, the maximum change of theshadow angle of tube I9 being approximately the same Whether thereceived wave signal has weak intensity or relatively strong intensity.For this reason, the tuning indications thus provided enable as high an`accuracy of tuning of the receiver to WaveA signals of weak intensityas to Wave signals of strong intensity, particularly in that the maximumresponse of the indicator system need no longerbe reserved, asheretofore necessary, for the highest intensity wave signal to beencountered in the operation of the receiver. t

Fig. 5 is a circuit diagram, partly schematic, of a portion of aWave-signal receiver of the amplitude-modulation type embodying `thepresent invention in a modied form. The present are' rangement isessentially similar to that of Fig, 1,'

9 similar Acircuit elements being designated Aby similar .referencenumerals and analogous circuit elements being designated-by similar.reference numerals primed, except ythat lthe .receiver includes anamplitude detector and A. V. C. supply l'forf deriving theamplitude-modulation components of a received wave signal and forderiving` aconventional A. V. C. bias. The tuning indicator tube I9'ofthe present .arrangement is of Aaftype conventionally us'ed inamplitude-modulation'relceivers and may, for example, vbe of the 6E5type which includes a triode section comprising a cathode 23.', acontrol electrode 45, and ananode..

The anode hasv internally connectedftheretoa defiecting electrode 24 andthe indicator tube Vincludes a target .electrode 22' .cooperatingWith'the deilecting electrode. The anode 46 is connected to the target.electrode V22 through a resistor 41- and the target electrode isenergized through the that of theoverallband-.pass characteristicofthereceiver.forpexample a pass band of tWofor three kilocycles Where thereceiver passband is ,kilocycles. The resonant ycircuit 43. -isienclosed Within a wave-signal shield, indi'catedby the :broken linesurrounding it, to reducezdirect pickfupbythe circuit of Wave-'signal,energyfand is coupled to the'cutput circuit-,ofthe amplifier' I5 Aby asmall coupling condenser 50..'of--one` or two in icromicroiaradscapacitance; f This small value ofV capacitanceis desirable .tominimizethe reaction of the resonant circuit 49 on the resonant couplingcircuits of the units I5 andl.. Afrecti*A ner device 5! and rectifierloadimpedarrcacomprising aresistor 52 and shunt condenserV 53, are

serially connected across the resonant circuit 49.

The resistor 52 preferably has avalueof resist-i ance Aof severalmegohms so that it does noteppreciablyload, and thereby decrease theQ;of, The condenser 53 has` the resonant. circuit 49. suflicientcapacitance that the time constant of this condenser and the resistor 52is long in comparison With the period of the lowest-,frequencymodulation component of the received Wave signal so that the modulationcomponents are 4effec,-

tively removed by the condenser 53 and resistor 52. The resistor 52 andcondenser 53 are connected between the controlelectrode 45 and thecathodef23' of the indicator tube I9.

The operation of this modied form of thevin vention is essentiallysimilar to that of Fig. 1.v In.

considering its operation, reference vis madeto the curves of Fig. 6Where curve N represents the band-pass characteristic of the receiver.-for a received Wave signal of relatively strong intensity andj curveOthat for a receivedl Wave signal of relatively Weaklintensity. Thisband-pass characteristic isassumed to have a relatively broad andnearly.at top over the frequency range f1. to fz centered upon the meanintermediate frequency/fo". Similarly, the band-pass character-,- isticof;the resonant vcircuit IltisV represented by the curve-P, Fig. 6for areceived Wave; signal o-strong intensity and by curve Rifor a receivedWave lsignal of relatively Weak intensity. Itwill. bessen that .theresonant. circuit 4.9 .is .tuned to...

1%0 the. meanintermediate ifre'qu'ency fo' and that .its band-passcharacteristic ris much narrower than that of the receiver.

The A.YV. C. bias developed by the A. V. C. supply of unit I6 has avalue Which, as the receiveris ytuned across a given received Wavesignal, varies in accordance with Vthe Aband-pass characteristic .of thereceiver. VvIt'vvill be thus apparent that curves N and fO:also'represent (the magnitude o'i A. V. C. lbias developed, Withituningof-t'he receiver, respectively to a strong `wave signal and to a weakWave signal. This A. V. C. bias so controls the' potentials of the.screen elec.- trode el :of-the tube 3'4 'andof the target electrode22". and anodeM ofthe indicator tube 19'., `for reasons -po-inted out inconnection WithFig. 1, that the curvesNf-and O may also be lconsideredto represent the variation of energzation o'f lthe specified yelectrodesof these tubes With v`tuning ofthe receiver across a strongreceived-'Wavesige nal and a weak received .Wave signal', respec-vtively.l l

it will thus v'beseen vthat the energizationsyof. the target electrode*22'l andi anode'46 'of-the indicator -tube- I9 remain; substantially`constant plained in'y connection withV vthe operation "of-` the.

Fig. -l arrangement.

The `tuning -signalf'supply system4'8 rectifies the Wave-signal energyv.applied thereto 'from the outputcircuit-of` theintermediatefrequencyam? plier l5 to develop across its load-impedance52.53 a unidirectional potential or tuningsign'al, free frommodulation*component/s, which' ris 'ap-.- plied to `the control:Velectrode 4510i the indicator tube? t5 to provide a tuning rindication.'lSince this vtuning 'signal' changes rapidly in magnitude over thetuning range f1 to fz' of thereceifver, and has .arriaiximumv value-atthe `mean intermed`iate frequency1 fof, Whereas .the Yenergizationof thetuning findicator tube -I-9vl is substantially f ,'con.- sta-nt overthistuning'range, it Wil-l be apparent that the entiretuning:indication. is,effected'along one of .teresponse curves J, K, E; or Lof Fig. 3y

as .established bythemagnitudeof thefA. V; C. bias-developed byunit I6andint-'hus by` the .intensitycff a received 'Wave signal.

of relatively'. Weak intensity, f for example one Which'establishes aisensitivity of" thev indicator tube I9' asf-represented by curve JofFig.- 3,' causes al sinaller tuning signalmtobe :developed bythe supplysystem 48. -The latter'signal'vmay.

be represented; for example;4 by the curve Rf of f Fig. 6. Now-while thermaximum magnitude-of thisrsignal is relativelysmall, it Will-bev notedthat the response 'sensitivity ofthe indicator tube 19", f

represented .bycurve J of Fig.- 3,' isk veryahighfso thatathe -smalltuning signalis able' toproduce a. large change of shadow-angleof-theindicator tube.` On theother-hand, arec'eivedwave sign-alof--relatively strong intensity, Whichfor example establishesasensitivity of the indicatortuberrl as represented by curve.. Leof Fig.3g-produces a larger tuning signalin-...the system 48; lfor example ysuchas that .represented vby curve lllof Fig..-6;.ls o

that the, larger signalis effective :to` produce a` large. changeoithershadowfangle Cifthe indicator` tubel 9. Inv practice.. thecircuitcomponen-osg ot the .tuning indicator zsystemmay. beaso,4selected..

that-bhe tuning indicaties rrevifled-rby'-thini `11 dic'atcr tube I9,"at the vmean intermediate frequency fe is substantially the same for.received Wave signals of Weak intensity as for received Wave signals ofstrong intensity. There consequently is no necessity for so operatingthe tuning indicator system that the maximum response of the system bereserved for the highest intensity Wave signal to be encountered in theoperation of the receiver.

It may be noted that the anode 46 of the indicator tube I9 is alsoenergized from the screen electrode 4| cf the repeater tube 34, thuseffecting a greater amplification of the tuning signal applied to thecontrol electrode 45 for higher intensity Wave signals. In certainapplications, it may be desirable that the anode 48 of tube I9' beenergized through the resistor 41 from a source of potential +B, ratherthan from the screen electrode 4| in order to maintain uniform theamplification provided by the triode section 23', 45 and 46 of tube I9.

Experience has shown that for uniformity of tuning indication over awide range of received wave-signal intensities, it is preferable thatthe A. V. C. supply of unit i6 be of the conventional delay-bias type.The value of delay bias to be used is established with relation to theintensity of a relatively weak intensity Wave signal such as thatl whichcauses operation of the indicator tube IS along curve J of Fig. 3. Forthis Wavesignal intensity. the value of delay bias used is preferablysuch that no A. V. C. bias is developed by the A. V. C. supply of unitI6 until the shadow angle of tube I9' has closed to approximately 45degrees'while tuning the receiver toward the wave signal.

`An additional operating characteristic of both the Figs. land 5 tuningindicator systems may be mentioned. This relates, as explained above inconnection with thearrangement of Fig. 1 to the change of brightness offluorescence of the target electrode 22 or 22 With the intensity of areceived wave signal. That is, Wave signals of larger intensity effectan increase of the target luminous intensity in accordance with the A.V. C. bias developed by the supply system of unit I6 or I6 thus furtherto aid in the tuning operation of the receiver. For example, While tun-Aing toward a desired wave signal an increase of luminous'intensity ofthe target electrode at once provides an indication that the desiredWave signal is being received even though no tuning indication is yetprovided by the indicator tube. The tuning operation is then completedby the indication furnished by the latter tube.

Fig. 7 is acircuit diagram, partly schematic, representing anadditionally modied form of the invention essentially similar to that ofFig. 5. Similar circuit elements are designated by similar referenceAnumerals and analogous elements by similar reference numerals doubleprimed. Here the indicating device I9" of the present arrangementcomprises an indicating meter. The latter has a held-energizing Winding54 included in the cathode circuit of the vacuumt'ube repeater 34 andhas a movable winding 55 mechanically connected to an indicating needley58 Yand coupled to the tuning signal supply 48.

The operation of this modified form of the invention is essentiallysimilar to that of Fig.` 5 except that the automatic-volume-control orA. V. C. bias applied to the control electrode 35 of the vacuum-tuberepeater 34 efiects a change of the space currents of both the anode 31and screen electrode 4|. Since the space currents of these electrodesflow through the cathode circuit of tube 34 and thus through the fieldWinding 54 of the indicating device I9", there is effected a change ofsensitivity of the device I9 withV changes of Wave-signal intensity.Thus received wave signals of large intensity, which produce a large A.V. C. bias and effect a substantial reduction of the space current ofthe repeater 34, effect a correspondingly large reduction of theelectromagnetic field produced by the meter winding 54. The large tuningsignal then applied to the deecting Winding 55 effects Va movement ofthe indicating needle 56 through ap.- proximately the same angle aswould occur with a received wave signal of much lesser intensity which,in developing a smaller A. V. C. bias, permits a larger energizingcurrent to flow through the winding 54 and alarger magnetic eld to bedeveloped thereby. 'I'he operation of this modied form of the inventionis otherwise essentially similar to that of Fig. 5 and will not berepeated.

It will be apparent from the above description of the invention that atuning indicator system embodying the invention hasv an indicatingsensitivity varying inversely with the intensity of a received wavesignal so that it provides approximately the same magnitude ofindication over a. wide range of received wave signal intensities. Thetuning indicator system of the invention has the additional advantagethat it is of simple and inexpensive circuit arrangement involving aminimum of circuit components.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it Will be obvious to thoseskilled in the art that various changes and modifications may be madetherein Without departing from the invention, and it is, therefore,aimed-'to cover all such changes and modifications as fall within theYtrue spirit and scope of the invention.

What is claimed is:

1'. A'tuning indicator system for a Wave-signal receiver including anadjustable tuning means comprising, an input circuit adapted to haveapplied thereto a control signal the magnitude of which varies with thedegree of mistuning of said receiver over individual tuning ranges oneither side of a received Wave signal, a tuning indicator coupled tosaid input circuit and responsive to said control signal for indicatingsaid degree of mistuning, and means for deriving a control effect themagnitude of which varies much less rapidly with said degree ofmistuning than does said control signal and for utilizing said controleffect to vary inversely With the intensity of said received Wave signalthe sensitivity of response of said indicator to said control signal toreduce the sensitivity of indication thereof with increasing intensitiesof said received Wave signal.

2. A tuning'indicator system for a wave-signal receiverincluding anadjustable tuning means comprising, an input circuit adapted to haveapplied thereto a control signal the magnitude of which varies both withthe intensity of a received Wave signal and with the degree of mistuningof said receiver over individual tuning ranges on either side of saidreceived Wave signal, a tuning indicator coupled to said input circuitand responsive to said control signal for indicating said degree ofmistuning, and means for deriving a control effect the magnitude ofwhich varies with the intensity of said received wavesignal butvariesmuch lessrapidly with said` degree ofrrmi'stuning than does saidcontrol signal andfor utilizing said control effect to vary inverselywith the magnitude thereof the sensitivity. of response of saidindicator to said control signal to reduce the sensitivity ofindicationthereof with increasing intensities of said received wavesigna-l.

3.' A tuningindicator system for a Wave-signal receiver. including anadjustable tuning means comprising, an input circuit adapted to' haveapplied thereto a control signal the magnitude andv polarityv of whichvary with the degree and direction, respectively, of mistuning of saidreceiver over individual tuning ranges on either side of a received wavesignal, a tuning indicator coupled to said input circuit and responsiveto said control signal for indicating said degree and direction ofmistuning, and means for deriving a control eiect the magnitude of Whichvaries much lessrapidly with said degree of mistuning than doessaidcontrol signal and for utilizing said control effect to varyinversely with the intensity of said received Wave signal thesensitivity of response of said indicator to said conor trol signal toreduce the sensitivity of indication thereof with increasing intensitiesof said received 'Wave signal.

4. A tun'ingindicator system for a Wave-signal receiver including anadjustable tuning means comprising, an input circuit adapted to haveapplied thereto a control signal the magnitude of which varies with thedegree lof mistuning of said receiver over individual tuning ranges oneither side of a received Wave signal, a cathode-ray tube tuningindicator having input electrodes coupled to said input circuit andresponsive to said control signal for indicating said degree ofmistuning, and means for deriving a control effect the magnitude of.which Vari-es much less rapidly with said degree of ymistuning than doessaid control signal and-forutilizing said control eiect to varyinversely with the magnitude thereof the energize.- tion of saidcathode-ray tube so toI control the sensitivity of response of saidindicator to said control signal as to reduce the sensitivity ofindication thereof with increasing intensities of said received Wavesignal.

5. A tuning indicator system for a wave-signal receiver including anadjustable tuning means comprising, an input circuit adapted tol haveapplied thereto a control signal the magnitude of which varies with thedegree of mistuning `of said receiver over individual tuning ranges oneither side of a received Wave signal, a cathode-ray tube tuningindicator having an anode and including input electrodes coupled to saidinput circuit and responsive to said control signal for indicating saiddegree of mistuning, and means for deriving a control effect themagnitude of which varies much less rapidly with said degree ofmistuning than does said control signal and for utilizing said controleffect to vary inversely with the magnitude thereof the energization ofsaid anode to reduce the sensitivity of indication of said indicatorwith increasing intensities `of said received Wave signal.

6. A tuning indicator system for a Wave-signal receiver including anadjustable tuning means comprising, an input circuit adapted to haveapplied thereto a control signal the magnitude oi which varies with thedegree of mistuning .of said receiver over individual tuning ranges oneither side of a received wave signal, a Icathode-ray tube tuningindicator having a cathode-ray target elecdoes said control signal andfor utilizing said.

control effect to vary inversely With the intensity of said receivedwave signal the energization of target electrode to reduce thesensitivity nf indication of said indicator with increasing ntensitiesoi said received Wave signal.

7. A tuning indicatorsystem for a Wave-signal receiver including anadjustable tuning means comprising, an input circuit adapted to haveapplied thereto a control signal the magnitude of which varies with thedegree of mistuning of said receiver over individual tuning ranges oneither side oi a received Wave signal, a tuning indicator coupled tosaid input circuit and responsive to said control signal for indicatingsaid degree of mistuning, a vacuum-tube repeater, means for deriving acontrol effect the magnitude of which varies much less rapidly with saiddegree of mistuning than does said control signal and for Autilizingsaid contnol leffect to vary inversely-withv the intensity of saidreceived Wave signal an operating characteristic of said repeater, andmeans `responsive Vto variations of said operating characteristic forcontrolling in accordance therewithl the sensitivity of response of saidindicator to said control signal to reduce the sensitivity of indicationthereof with increasing intensities of said plied thereto a controlsignal the magnitude of y which varies with the degree of mistuning ofsaid receiver over individual tuning ranges oneithert side of a receivedWave signalja tuning indicator coupled to said input circuit andresponsive to said control signal for indicating said degree ofmistuning, a vacuum-tube repeater, means for deriving a control eiectthe magnitude of which varies muclh less rapidly with said degree ofmistuning than does said control signal and for utilizing said `controleffect to vary inversely with the intensity of `said received Wavesignal the transconductance yof said repeater, and means responsive tovariations of said transconductance for controlling in accordancetherewith the sensitivity of response of said indicator to said contnolsignal to reduce the sensitivity of indication thereof With increasingintensities of said received Wave signal.

9. A tuning indicator system for a Wave-signal receiver including anadjustable tuning means comprising, an input circuit adapted to haveapplied thereto a control signal the magnitude of which varies with thedegree of mistuning of said receiver over individual tuning ranges oneither side o'f a received Wave signal, a tuning indicator coupled tosaid input circuit and responsive to said control signal for indicatingsaid degree of mistuning, -a vacuum-tube repeater having a positivelyenergized electrode, means for deriving a control effect the magnitudeof which varies much. less rapidly with said degree of mistuning thandoes said. control signal and for utilizing said control eiect to varyinversely with the intensity of said received Wave signal theenergization of said electrode, and an energizing circuit for energizingsaid indicator from said positively energized electrode to varyinversely with the intensity of said received Wave signal thesensitivity of response to said indicator to said control signal toreduce the sensitivity of indication thereof with increasing intensitiesof said received Wave signal.

10. A tuning indicator system for a Wave-signal receiver including anadjustable tuning means and a gain-controllable Wave-signal ampliercomprising, an input circuit adapted to have applied thereto a controlsignal the magnitude of which varies with the degree of mistuning ofsaid receiver over individual tuning ranges on either side of a receivedWave signal, a tuning indicator coupled to said input circuit andresponsive to said control signal for indicating said degree ofmistuning, means for deriving a control effect the magnitude of whichvaries much less rapidly with said degree of mistuning than does saidcontrol signal and for utilizing said control effect to vary inversely7With the intensity of said received Wave signal the gain of saidampliiier, and 'means responsive to variations of the gain of saidamplier for controlling in accordance therewith the sensitivity ofresponse of said indicator to said control signal to reduce thesensitivity of indication thereof with increasing intensities of saidreceived Wave signal.

11. A tuning indicator system for a Wave-signal receiver including anadjustable tuning means and having a relatively broad band-passcharacteristic for received wave signals comprising, an input circuitadapted to have applied thereto a control signal the magnitude of Whichover at least the central portion of said band pass of said receivervaries rapidly With the degree of mistuning of said receiver overindividual tuning ranges on either side of a received wave signal, atuning indicator coupled to said input circuit and responsive to saidcontrol signal for indicating said degree of mistuning, and means forderiving a control eiect the magnitude of which over said pass band ofsaid receiver varies much less rapidly with said degree of mistuningthan does said control signal and for utilizing said control effect tovary inversely with the intensity of said received Wave signal thesensitivity of response of said indicator to said control signal toreduce the sensitivity of indication thereof with increasing intensitiesof said received Wave signal.

l2. A tuning indicator system for a vWave-signal receiver including anadjustable tuning means and having a relatively broad fband-passcharacteristic for received Wave signals comprising, means including asharply resonant circuit having a lband-pass characteristicsubstantially less than that of said receiver for deriving a controlsignal the magnitude olf Which over at least the central portion of saidpass band of said receiver varies rapidly with the degree of mistuningof said receiver over individual .tuning ranges on either side of areceived Wave signal, a tuning indicator coupled to said means andresponsive to said control signal for indicating said degree ofmistuning, and means for deriving a control effect the magnitude ofwhich over said pass band of said receiver varies much less rapidly withsaid degree of mistuning than does said control signal and for utilizingsaid control effect to vary inversely with the intensity of saidreceived wave signal the sensitivity of response of said indicator tosaid control signal to reduce the sensitivity of indication thereof withincreasing intensities of said received wave signal.

HAROLD L. BLAISDELL.

REFERENCES CITED The following references are oi record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 2,164,979 Wilhelm July 4, 19392,334,473 Carlson Nov. 16, 1943

